U.S. patent number 7,898,218 [Application Number 11/804,495] was granted by the patent office on 2011-03-01 for power supply topologies with pwm frequency control.
This patent grant is currently assigned to 02Micro International Limited. Invention is credited to Chien Kung, Chun-Hsi Lin, Footshen Wong, Chen-Hsiang Yu.
United States Patent |
7,898,218 |
Lin , et al. |
March 1, 2011 |
**Please see images for:
( Certificate of Correction ) ** |
Power supply topologies with PWM frequency control
Abstract
A power supply topology with pulse width modulation frequency
control allows the use of an inductor with higher inductance in a
converter. By controlling the switching frequency of the pulse
width modulation signal, the inductor can achieve high efficiency
during a light load condition and is also suitable for a heavy load
condition.
Inventors: |
Lin; Chun-Hsi (Yi-Lan Shien,
TW), Wong; Footshen (Singapore, SG), Kung;
Chien (Taipei, TW), Yu; Chen-Hsiang (Taipei,
TW) |
Assignee: |
02Micro International Limited
(Grand Cayman, KY)
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Family
ID: |
39168898 |
Appl.
No.: |
11/804,495 |
Filed: |
May 17, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20080061759 A1 |
Mar 13, 2008 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60844140 |
Sep 12, 2006 |
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Current U.S.
Class: |
320/134; 363/19;
363/141; 363/142; 320/142 |
Current CPC
Class: |
H02M
3/157 (20130101); Y02B 70/10 (20130101); H02M
1/0032 (20210501) |
Current International
Class: |
H02J
7/00 (20060101) |
Field of
Search: |
;320/134,140,141,142
;307/37,73 ;363/165 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Tso; Edward
Assistant Examiner: Williams; Arun
Parent Case Text
RELATED APPLICATION
This application claims priority to U.S. Provisional Application
No. 60/844,140, filed on Sep. 12, 2006, which is hereby
incorporated by reference in its entirety.
Claims
What is claimed is:
1. A converter comprising: a generator generating a pulse width
modulation signal for controlling an inductor; and a control
circuit coupled to said generator for controlling a switching
frequency of said pulse width modulation signal, wherein a first
switching frequency is selected when a load current is less than a
predetermined current level, and wherein a second switching
frequency that is greater than said first switching frequency is
selected when said load current is greater than said predetermined
current level, wherein a peak-to-peak ripple current of said
inductor decreases from a first ripple current level to a second
ripple current level that is less than said first ripple current
level in response to said switching frequency of said pulse width
modulation signal if said load current increases from a first
current level that is less than said predetermined current level to
a second current level that is greater than said predetermined
current level.
2. The converter as claimed in claim 1, wherein said control
circuit comprises an internal control circuit operable for
monitoring said load current and generating a first frequency
control signal to said generator for controlling said switching
frequency.
3. The converter as claimed in claim 2, wherein said control
circuit comprises an external control circuit operable for
receiving an external control signal and generating a second
frequency control signal to said generator for controlling said
switching frequency.
4. The converter as claimed in claim 3, further comprising a
communication signal line between said internal control circuit and
said external control circuit.
5. The converter as claimed in claim 3, wherein said generator
comprises an oscillator operable for receiving said first frequency
control signal and said second frequency control signal, and for
generating a ramp signal.
6. The converter as claimed in claim 5, wherein said internal
control circuit further generates a current control signal to said
generator for adjusting a duty cycle of said pulse width modulation
signal.
7. The converter as claimed in claim 6, wherein said generator
comprises an amplifier operable for receiving said ramp signal and
said current control signal, and for generating said pulse width
modulation signal.
8. The converter as claimed in claim 1, wherein said load current
is selected from a first load current and a second load current
that is greater than said first load current.
9. The converter as claimed in claim 1, further comprising a switch
coupled to said inductor for receiving said pulse width modulation
signal.
10. A method for powering a load, comprising: monitoring an amount
of load current; controlling a switching frequency of a pulse width
modulation signal to decrease a peak-to-peak ripple current of an
inductor from a first ripple current level to a second ripple
current level that is less than said first ripple current level if
said load current increases from a first current level that is less
than a predetermined current level to a second current level that
is greater than said predetermined current level; wherein said
pulse width modulation signal has a first switching frequency when
said load current is less than said predetermined current level,
and wherein said pulse width modulation signal has a second
switching frequency that is greater than said first switching
frequency when said load current is greater than said predetermined
current level.
11. The method as claimed in claim 10, further comprising:
receiving a frequency control signal for controlling said switching
frequency.
12. The method as claimed in claim 11, wherein said frequency
control signal is generated according to an external control
signal.
13. The method as claimed in claim 12, further comprising:
generating a ramp signal in response to said frequency control
signal.
14. The method as claimed in claim 13, further comprising:
receiving a current control signal for adjusting a duty cycle of
said pulse width modulation signal, wherein said pulse width
modulation signal is generated according to said current control
signal and said ramp signal.
15. An electronic device comprising: a load; and a converter
coupled to said load, comprising: an inductor; a generator
generating a pulse width modulation signal for controlling said
inductor; an output for providing a load current to said load; an
internal control circuit operable for monitoring said load current
and for generating a first frequency control signal to said
generator for controlling said switching frequency; and an external
control circuit operable for receiving an external control signal
and for generating a second frequency control signal to said
generator for controlling said switching frequency, wherein a first
switching frequency is selected when said load current is less than
a predetermined current level, wherein a second switching frequency
that is greater than said first switching frequency is selected
when said load current is greater than said predetermined current
level, wherein a peak-to-peak ripple current of said inductor
decreases from a first ripple current level to a second ripple
current level that is less than said first ripple current level in
response to said switching frequency of said pulse width modulation
signal if said load current increases from a first current level
that is less than said predetermined current level to a second
current level that is greater than said predetermined current
level.
16. The electronic device as claimed in claim 15, wherein said
internal control circuit transmits information to said external
control circuit.
17. The electronic device as claimed in claim 15, wherein said
external control circuit transmits information to said internal
control circuit.
18. The electronic device as claimed in claim 15, wherein said
internal control circuit further generates a current control signal
to said generator for adjusting a duty cycle of said pulse width
modulation signal.
19. The electronic device as claimed in claim 15, wherein said
generator comprises an oscillator operable for receiving said first
frequency control signal and said second frequency control signal,
and for generating a ramp signal.
20. The electronic device as claimed in claim 19, wherein said
generator comprises an amplifier for receiving said ramp signal and
said current control signal, and for generating said pulse width
modulation signal.
21. The electronic device as claimed in claim 15, further
comprising a switch coupled to said inductor for receiving said
pulse width modulation signal.
Description
TECHNICAL FIELD
This invention relates to power management topologies and in
particular to power management topologies with pulse width
modulation (PWM) control able to support multiple load level
applications.
BACKGROUND ART
When choosing an inductor in a switching circuit (e.g., boost/buck
converter), there are some concerns including inductance, DC-rating
current and direct current resistance (DCR) value. DC-rating
current is one of the basic characteristics of an inductor, which
represents the maximum current allowed to flow through the
inductor. DC-rating current is determined by the inductance,
inductor size, and wire, etc. For a given inductor size, the DCR
value is directly proportional to the inductance and the DC-rating
current is inversely proportional to the inductance.
For a DC/DC boost converter, the efficiency during a light load
condition is also directly proportional to the inductance. In order
to improve the efficiency, there is a need to choose an inductor
with higher inductance. However, as noted above, the higher the
inductance, the lower the allowed DC-rating current will be. The
peak current through the inductor is equal to the summation of the
average current (maximum load current) and the peak ripple current
of the inductor. As such, an inductor with higher inductance may
not meet requirements when used under heavy load conditions. This
is because the peak current through the inductor significantly
increases as the average current (maximum load current) increases
during the heavy load condition and the current through the
inductor may exceed the allowed DC-rating current limit. Therefore,
an inductor with higher inductance may not be suitable for a high
current/heavy load condition.
There are at least two requirements in choosing an inductor in a
boost/buck DC/DC converter. First, the inductor needs to be able to
work during the high current condition (the peak current of the
inductor should be within the allowed DC-rating current limit).
Second, the inductor needs to have high inductance to achieve high
efficiency under the low current condition. Since the DC-rating
current is inversely proportional to the inductance, it is
difficult to choose an inductor that meets both requirements.
SUMMARY
In accordance with one embodiment of the present invention, a
converter comprises a generator that generates a pulse width
modulation signal for controlling an inductor, and a control
circuit coupled to the generator that controls a switching
frequency of the pulse width modulation signal. A first switching
frequency is selected when a load current is less than a
predetermined current level, in one embodiment. A second switching
frequency that is greater than the first switching frequency is
selected when the load current is greater than the predetermined
current level, in one embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
Features and advantages of embodiments of the claimed subject
matter will become apparent as the following Detailed Description
proceeds, and upon reference to the Drawings, wherein like numerals
depict like parts, and in which:
FIG. 1 shows a block diagram of a converter with pulse width
modulation frequency control, in accordance with one embodiment of
the present invention.
FIG. 2 shows another block diagram of a converter with pulse width
modulation frequency control, in accordance with one embodiment of
the present invention.
FIG. 3 shows a flowchart of a method for implementing a converter
with pulse width modulation frequency control, in accordance with
one embodiment of the present invention.
FIG. 4A shows a waveform representing the current through an
inductor during a light load condition, in accordance with one
embodiment of the present invention.
FIG. 4B shows a waveform representing the current through an
inductor during a heavy load condition, in accordance with one
embodiment of the present invention.
DETAILED DESCRIPTION
Reference will now be made in detail to embodiments of the present
invention. While the invention will be described in conjunction
with these embodiments, it will be understood that they are not
intended to limit the invention to these embodiments. On the
contrary, the invention is intended to cover alternatives,
modifications and equivalents, which may be included within the
spirit and scope of the invention as defined by the appended
claims.
Furthermore, in the following detailed description of the present
invention, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. However,
it will be recognized by one of ordinary skill in the art that the
present invention may be practiced without these specific details.
In other instances, well known methods, procedures, components, and
circuits have not been described in detail as not to unnecessarily
obscure aspects of the present invention.
In one embodiment, the present invention provides a power
management topology with pulse width modulation frequency control.
Advantageously, the frequency of a pulse width modulation signal
can be adjusted according to different load conditions, in one
embodiment. Such topology allows the use of an inductor with higher
inductance which is able to achieve high efficiency during a light
load condition and is also suitable for a heavy load condition.
FIG. 1 shows a block diagram of a converter 100 with pulse width
modulation frequency control, in accordance with one embodiment of
the present invention. As shown in FIG. 1, the converter 100
includes a generator 102 (also referred as the frequency control
block) for generating a pulse width modulation signal 132 for
controlling an inductor 110, and a control circuit 108 coupled to
the generator 102 for controlling a switching frequency of the
pulse width modulation signal 132. The inductor 110 is coupled to
an input 172 and an output 170.
The converter 100 in the present invention not only supports a
single output channel, but also supports multiple output channels.
For example, a load 140A and a load 140B are both coupled to the
output terminal 170, in one embodiment. The load 140A and the load
140B may include, but are not limited to light-emitting diodes
(LEDs). The level of the load current 160A flowing through the load
140A and the level of the load current 160B flowing through the
load 140B is different, in one embodiment. For example, the level
of the load current 160A (high current sink) is greater than the
level of the load current 160B (low current sink).
The switching frequency of the pulse width modulation signal 132 is
adjusted according to different load conditions. Advantageously, a
first switching frequency f1 (e.g., 1 MHz) is selected when a load
current (load current 160A and/or load current 160B) is less than a
predetermined current level I0. A second switching frequency f2
(e.g., 4 MHz) that is greater than the first switching frequency f1
is selected when the load current (load current 160A and/or load
current 160B) is greater than the predetermined current level
I0.
The current through the inductor 110 is controlled by the pulse
width modulation signal 132. As a result, a peak-to-peak ripple
current of the inductor 110 reaches a first ripple current level
I.sub.sw1 when the load current is less than the predetermined
current level I0. The peak-to-peak ripple current of the inductor
110 reaches a second ripple current level I.sub.sw2 that is less
than the first ripple current level I.sub.sw1 when the load current
is greater than the predetermined current level I0.
In one embodiment, the control circuit 108 includes an internal
control circuit 104 (also referred as the current control block).
The internal control circuit 104 is operable for monitoring the
load current (160A and 160B) and generating a first frequency
control signal 126 to the generator 102 to control the switching
frequency of the pulse width modulation signal 132.
More specifically, when the internal control circuit 104 detects
that the load current (160A and/or 160B) is less than a
predetermined current level I0, the first frequency control signal
126 will control the generator 102 to generate a pulse width
modulation signal 132 with a first switching frequency f1 (e.g., 1
MHz), in one embodiment. When the internal control circuit 104
detects that the load current (160A and/or 160B) is greater than
the predetermined current level I0, the first frequency control
signal 126 will control the generator 102 to generate a pulse width
modulation signal 132 with a second switching frequency f2 (e.g., 4
MHz) that is greater than the first switching frequency f1, in one
embodiment.
Furthermore, the internal control circuit 104 can generate a
current control signal (not shown) to the generator 102 for
adjusting a duty cycle of the pulse width modulation signal 132, in
one embodiment.
In one embodiment, the control circuit 108 includes an external
control circuit 106 (also referred as the digital control block).
The external control circuit 106 is operable for receiving an
external control signal and generating a second frequency control
signal 124 to the generator 102 to control the switching frequency
of the pulse width modulation signal 132.
In one embodiment, the external control signal can be a digital
control signal transmitted via an I.sup.2C bus including a clock
signal line 150A and a data signal line 150B. As a result, the user
is able to control the switching frequency of the pulse width
modulation signal 132 by transmitting information via the external
control signal line (clock signal line 150A and data signal line
150B). Such information may include, but is not limited to the
desired load current level.
Advantageously, there is a communication signal line 130A between
the internal control circuit 104 and the external control circuit
106. In one embodiment, the communication signal line 130A is
configured to transmit information from the internal control
circuit 104 to the external control circuit 106. Such information
may include, but is not limited to load current level and the
switching frequency of the pulse width modulation signal 132.
As a result, the generator 102 receives the first frequency control
signal 126 and/or the second frequency control signal 124, and
generates a pulse width modulation signal 132 accordingly. The
frequency of the pulse width modulation signal 132 can be
determined by the first frequency control signal 126, in one
embodiment. The frequency of the pulse width modulation signal 132
can be determined by the second frequency control signal 124, in
another embodiment.
Accordingly, in accordance with one embodiment of the present
invention, the pulse width modulation signal 132 can be controlled
by an analog control circuit which is the internal control circuit
104 and/or a digital control circuit which is the external control
circuit 106.
FIG. 2 shows another block diagram of a converter 200 with pulse
width modulation frequency control, in accordance with one
embodiment of the present invention. Elements that are labeled the
same as in FIG. 1 have similar functions and will not be
repetitively described herein for purposes of brevity and
clarity.
As shown in FIG. 2, the generator 102 includes an oscillator 202
and an amplifier 204, in one embodiment. The generator 202 receives
a first frequency control signal 126 and/or a second frequency
control signal 124, and generates a ramp signal 212, in one
embodiment. For example, the oscillator 202 can generate a ramp
signal 212 with a first switching frequency f1 (e.g., 1 MHz) or a
ramp signal 212 with a second switching frequency f2 (e.g., 4 MHz)
depending on the first frequency control signal 126 and/or the
second frequency control signal 124.
The amplifier 204 can be used to receive the ramp signal 212 from
the oscillator 202 and receive a current control signal 226 from
the internal control circuit 104. The amplifier 204 compares the
ramp signal 212 with the current control signal 226, and generates
a pulse width modulation signal 132 for controlling a switch 220
via a driver 206, in one embodiment. The switch 220 is coupled to
the inductor 110. Therefore, the current through the inductor 110
is adjusted in relation to the pulse width modulation signal
132.
Advantageously, by increasing the switching frequency of the ramp
signal 212, the peak-to-peak ripple current of the inductor 110
decreases. More specifically, if the ramp signal 212 has a first
switching frequency f1 (e.g., 1 MHz), the switching frequency of
the pulse width modulation signal 132 is also equal to the first
switching frequency f1. As such, the peak-to-peak ripple current
through the inductor 110 will reach a first ripple current level
I.sub.sw1. If the ramp signal 212 has a second switching frequency
f2 (e.g., 4 MHz) that is greater than the first switching frequency
f1, the switching frequency of the pulse width modulation signal
132 is also equal to the second switching frequency f2. As such,
the peak-to-peak ripple current through the inductor 110 will reach
a second ripple current level I.sub.sw2 that is less than the first
ripple current level I.sub.sw1
Furthermore, the converter 200 includes a communication signal line
130A and a communication signal line 130B. In one embodiment, the
communication signal line 130A is configured to transmit
information from the internal control circuit 104 to the external
control circuit 106. Such information may include, but is not
limited to load current level and the switching frequency of the
pulse width modulation signal 132. In one embodiment, the external
control block 106 transmits information to the internal control
block 104 via the communication signal line 130B. Such information
may include, but is not limited to the switching frequency of the
oscillator 202 and the desired load current level.
FIG. 3 shows a flowchart 300 of a method for implementing a
converter with pulse width modulation frequency control, in
accordance with one embodiment of the present invention. FIG. 3
will be described in combination with FIG. 1 and FIG. 2.
In block 302, an amount of load current is monitored. In one
embodiment, the internal control circuit 104 monitors the load
current 160A and the load current 160B. In block 304, the generator
102 (frequency control block) receives a frequency control signal.
Such frequency control signal can be a first frequency control
signal 126 from the internal control circuit 104 or a second
frequency control signal 124 from the external control circuit 106,
in one embodiment.
In block 306, a ramp signal 212 is generated by an oscillator 202
in response to the frequency control signal (first frequency
control signal 126 and/or a second frequency control signal 124),
in one embodiment. In block 308, a current control signal 226 can
be received by an error amplifier 204 from the internal control
block 104. More specifically, the current control signal 226 is
used to determine the duty cycle of a pulse width modulation signal
132 for adjusting the load current, in one embodiment.
In block 310, a switching frequency of the pulse width modulation
signal 132 is controlled/adjusted. The pulse width modulation
signal 132 is generated by comparing the ramp signal 212 with the
current control signal 226. As such, the switching frequency of the
pulse width modulation signal 132 is determined by the frequency of
the ramp signal 212 from the oscillator 202, in one embodiment.
More specifically, the pulse width modulation signal 132 has a
first switching frequency f1 when a load current (160A and/or 160B)
is less than a predetermined current level I0. The pulse width
modulation signal 132 has a second switching frequency f2 that is
greater than the first switching frequency f1 when the load current
(160A and/or 160B) is greater than the predetermined current level
I0.
In block 312, a peak current of an inductor 110 is controlled. More
specifically, the peak-to-peak ripple current of the inductor 110
reaches a first ripple current level I.sub.sw1 when a load current
(160A and/or 160B) is less then the predetermined current level I0.
The peak-to-peak ripple current of the inductor 110 reaches a
second ripple current level I.sub.sw2 that is less than the first
peak-to-peak ripple current level I.sub.sw1 when the load current
(160A and/or 160B) is greater than the predetermined current level
I0.
Referring to the TABLE 1, examples of inductors' characteristics
are shown. As the inductance increases, the DC-rating current will
decrease as shown in the TABLE 1. Although an inductor with higher
inductance will provide higher efficiency under light load
condition, its allowed DC-rating current will be lower. For
example, there are two inductors: inductor A (Part No.
VLF3012AT-2R2M1R0) and inductor B (Part No. VLF3012AT-4R7MR74). The
DC-rating current (rated current) of inductor A is equal to 1 A.
The inductance of inductor A is equal to 2.2 uH. The DC-rating
current (rated current) of inductor B is equal to 0.74 A. The
inductance of inductor B is equal to 4.7 uH. The light load
efficiency of inductor A is equal to 67%. The light load efficiency
of inductor B is equal to 82%. The inductor peak current is usually
0.93 A when the inductor works under the high current/heavy load
condition at 1 MHz switching frequency, in one embodiment.
TABLE-US-00001 TABLE 1 ELECTRICAL CHARACTERISTICS Rated current(A)*
DC Based on Based on Inductance Inductance Test frequency
resistance(.OMEGA.) inductance temperature Part No. (.mu.H)
tolerance(%) (kHz) max. typ. change max. rise typ.
VLF3012AT-1R5N1R2 1.5 .+-.30 100 0.068 0.059 1.2 1.6
VLF3012AT-2R2M1R0 2.2 .+-.20 100 0.1 0.088 1.0 1.3
VLF3012AT-3R3MR87 3.3 .+-.20 100 0.13 0.11 0.87 1.2
VLF3012AT-4R7MR74 4.7 .+-.20 100 0.19 0.16 0.74 0.98
VLF3012AT-6R8MR59 6.8 .+-.20 100 0.27 0.23 0.59 0.83
VLF3012AT-100MR49 10 .+-.20 100 0.41 0.36 0.49 0.67
VLF3012AT-150MR41 15 .+-.20 100 0.62 0.54 0.41 0.54
VLF3012AT-220MR33 22 .+-.20 100 0.76 0.66 0.33 0.49
VLF3012AT-330MR27 33 .+-.20 100 1.3 1.1 0.27 0.38 VLF3012AT-470MR22
47 .+-.20 100 2.2 1.9 0.22 0.29
Advantageously, in accordance with one embodiment of the present
invention, the inductor B can be used to achieve higher efficiency.
More specifically, the switching frequency can be increased during
the high current/heavy load condition to lower the peak-to-peak
current of the inductor B. For example, the switching frequency can
be increased to 4 MHz during the high current/heavy load condition,
in one embodiment. As such, the peak-to-peak ripple current of
inductor B can be reduced to fall within the allowed DC-rating
current (0.74 A) during high current/heavy load condition.
Therefore, the inductor B can be used in the present embodiment
instead of inductor A by controlling the switching frequency of the
pulse width modulation signal according to different load
conditions.
FIG. 4A shows a waveform 302A representing the current through
inductor B during a light load condition, in accordance with one
embodiment of the present invention. FIG. 4A is described in
combination with FIG. 1 and FIG. 2. During the light load
condition, the generator 102 is controlled to generate a pulse
width modulation signal 132 with a first switching frequency f1
(e.g., f1=1 MHz). The generator 102 can be controlled by an
internal control circuit 104 or an external control circuit 106, in
one embodiment. As shown in FIG. 4A, the slope of the inductor
current is equal to the input voltage V.sub.in at input 172 divided
by the inductance L.sub.B (V.sub.in/L.sub.B). The inductor peak
current I.sub.p1 is equal to the summation of the average current
I.sub.ave1 and half of the peak-to-peak ripple current I.sub.sw1
(I.sub.p1=I.sub.ave1+I.sub.sw1/2).
FIG. 4B shows a waveform 302B representing the current through
inductor B during a heavy load condition, in accordance with one
embodiment of the present invention. FIG. 4B is described in
combination with FIG. 1 and FIG. 2. During the heavy load
condition, the generator 102 is controlled to generate a pulse
width modulation signal 132 with a second switching frequency f2
(e.g., f1=4 MHz) that is greater than the first switching frequency
f1. As shown in FIG. 4B, the slope of the inductor current is equal
to the input voltage V.sub.in at input 172 divided by the
inductance L.sub.B (V.sub.in/L.sub.B). The inductor peak current
I.sub.p2 is equal to the summation of the average current
I.sub.ave2 and half of the peak-to-peak ripple current I.sub.sw2
(I.sub.p2=I.sub.ave2+I.sub.sw2/2).
As shown in FIG. 4A and FIG. 4B, higher switching frequency
(f2>f1) can reduce the peak-to-peak ripple current
(I.sub.sw2<I.sub.sw1) of the inductor, in one embodiment.
Although the average current I.sub.ave2 during the heavy load
condition is greater than the average current I.sub.ave1 during the
light load condition, the inductor peak-to-peak ripple current
I.sub.sw2 during the heavy load condition is much less than the
inductor ripple current I.sub.sw1 during the light load condition.
Consequently, the peak current of inductor B can be reduced to
I.sub.p2 at the switching frequency f2 during high current/heavy
load condition, such that I.sub.p2 is within the DC-rating current
of inductor B (0.74 A). Therefore, inductor B can be used during
both heavy load and light load conditions to achieve high
efficiency, in accordance with one embodiment of the present
invention.
Accordingly, embodiments of the present invention provide power
management topologies with pulse width modulation frequency
control. Advantageously, the switching frequency of a pulse width
modulation signal can be adjusted according to different load
conditions, in one embodiment. During a heavy load condition, the
switching frequency will be increased (e.g., to 4 MHz) to reduce
the peak-to-peak ripple current of the inductor. During a light
load condition, the switching frequency will get back to the normal
value (e.g., 1 MHz) to reduce switching loss and to achieve higher
efficiency. Furthermore, a power management topology in accordance
with one embodiment of the present invention also supports multiple
output channels by one controller and one inductor in order to save
space and reduce cost.
While the foregoing description and drawings represent embodiments
of the present invention, it will be understood that various
additions, modifications and substitutions may be made therein
without departing from the spirit and scope of the principles of
the present invention as defined in the accompanying claims. One
skilled in the art will appreciate that the invention may be used
with many modifications of form, structure, arrangement,
proportions, materials, elements, and components and otherwise,
used in the practice of the invention, which are particularly
adapted to specific environments and operative requirements without
departing from the principles of the present invention. The
presently disclosed embodiments are therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims and their legal
equivalents, and not limited to the foregoing description.
* * * * *